1. Field of the Invention
The present invention relates to the field of digital cellular wireless telecommunications. More particularly, the invention relates to a telecommunications cell for a digital CDMA, wireless telecommunications network.
2. Description of the Prior Art
Sprint PCS and other companies offer wireless communication services using code division multiple access (CDMA) techniques. CDMA is a digital spread-spectrum modulation technique that digitizes wireless conversations and tags them with special codes. The digitized data is spread across the frequency band in a pseudo random pattern. Receiving mobile phones are instructed to decipher only the data corresponding to particular codes to reconstruct the signal. CDMA networks are superior to other wireless networks because they provide increased network capacity, fewer dropped calls because of better hand-off methods, improved voice clarity, improved privacy and transmission security, and enhanced services such as text messaging and data transmissions.
A typical CDMA PCS telecommunications cell includes a base station unit and three sector antennas that together provide wireless communications in three sectors of the cell each covering 120xc2x0. The base station unit uses a predefined set of sixty-four CDMA Walsh codes for each sector, with one of the codes used for pilot channel, another for synchronization, one commonly used for paging, and the remainder available for ordinary traffic.
In actual usage, however, all of the remaining channels cannot be used for traffic because of noise accumulated in the band due to a variety of reasons such as interference from adjacent cells and unused multi-path signals. With the distinct advantages of PCS CDMA communications, demand for service is substantial and in some cases, may exceed cell capacity. In the prior art, one of the solutions has been to add more base stations at the same cells to provide increased capacity. This is an expensive solution because it requires additional base stations and equipment.
The present invention solves the prior art problems discussed above and provides a distinct advance in the state of the art. In particular, the system hereof provides an improved telecommunications cell for a PCS CDMA telecommunications network.
The preferred cell includes a single base station unit and a plurality of antennas that configure the cell into a plurality of sectors. The base station controls transmission and reception over the antennas using selected ones of a defined set of CDMA codes for each of the sectors. Each sector preferably includes two antennas coupled with the base station. The base station is configured to divide the number of available Walsh codes or channels for each sector so that each antenna in each sector operates at a separate frequency and handles a portion of the Walsh codes or channels for the sector. This provides two transmission frequencies in each sector with a single base station, thereby increasing effective cell capacity by a factor of two without increasing the number of base stations.